What is a Thermocouple and How Does It Work?

If you have an older furnace that uses a conventional standing pilot light, you may have heard your technician mention a thermocouple at some point throughout the system’s lifespan. A thermocouple is an essential safety device in older furnaces, and if it encounters any problems it can completely shut down your system. Today we’re going to talk about what a thermocouple does, how it improves the safety of your furnace and some common things that can go wrong with it!

What is a thermocouple and how does it work?

A thermocouple’s primary responsibility is to monitor the performance of your furnace’s pilot light. One end of the thermocouple is attached to the line that supplies gas to the pilot light. This allows the device to close off the gas supply to your pilot light at any time. The other end of the thermocouple is a metal rod that points directly over the pilot light’s flame. This rod constantly reads the temperature of the flame.

The heat from the pilot light’s flame that is registered by the thermocouple’s metal rod provides a small voltage through the device that keeps the gas supply open. If the pilot light goes out, there will be no more heat to keep that voltage going and the gas supply will be shut off.

How does a thermocouple improve the safety of your furnace?

• Prevents gas buildup inside your furnace. If your pilot light goes out, there will be no flame to burn the gas that’s delivered to it. Without a thermocouple, that gas could build up inside your furnace. This can potentially cause a small explosion inside your furnace if the gas makes its way near your system’s burners. By shutting off the gas supply to your pilot light when the flame goes out, the thermocouple prevents this safety concern.
• Prevents gas leaks in your home’s air. Another issue with a pilot light going out is that the gas that was intended for the flame could leak into your home’s air, which is a health concern and can also cause fire hazards in other parts of your home. A thermocouple prevents this from happening by immediately shutting off the gas supply to your system as soon as it recognizes that the flame has gone out.

What can go wrong with your furnace’s thermocouple?

There are a couple things that can go wrong with a thermocouple that can affect the performance of your entire system. One common issue is dirt buildup. If you thermocouple gets dirty, it can get inaccurate temperature readings from your pilot light. This can cause your thermocouple to shut off your furnace’s gas supply even if the pilot light is still lit. You can avoid this issue by changing your air filter every month and scheduling a furnace clean and check every year.

It’s important to note that most thermocouples are not designed to last for the entire operating life of a furnace. As a result, they will need to be replaced once in a while. By scheduling a furnace tune-up every year, you can ensure that your thermocouple is always working and that it will be replaced proactively so that your furnace won’t suffer from downtime due to a thermocouple that’s on the fritz.

If you have any questions about how thermocouples work, or if you’d like a heating system serviced or installed in your home, contact Hydes, your Coachella Valley furnace installation and repair contractor.